Australasian Science: Australia's authority on science since 1938

The Criminal Brain

By Tim Hannan

Antisocial behaviour after brain injury is associated with lesions to a single neural network.

While it is well-known that previously law-abiding people sometimes exhibit criminal behaviour after suffering a brain injury, the areas of the brain most associated with such behaviour have not been clearly identified. Prior studies of brain-injured patients who have committed crimes have reported lesions in diverse brain regions, suggesting that no single area of the brain is critical to the development of antisocial or violent behaviour. Now, the first systematic review of a series of cases has found that all have suffered damage to a specific network of brain neurons, suggesting that such newly acquired criminal behaviour may be explained by a single neural network.

While criminal behaviour has many causes, prior neuropsychological research has shown that some people developed criminal behaviour after sustaining brain damage through a head injury, stroke, tumour or dementia. A classic case often referenced is Charles Whitman, a former US marine who murdered his wife, mother and 14 other people after a tumour developed in his right temporal lobe. Prior to these events, he had not displayed any general cognitive difficulties, although changes in his mood, personality and moral judgement were evident. In a letter written on the day before the killings, he commented: “It was after much thought that I decided to kill my wife, Kathy… I love her dearly, and she has been as fine a wife to me as any man could ever hope to have. I cannot rationally pinpoint any specific reason for doing this.”

While brain damage may contribute to violent or criminal behaviour, it cannot be inferred that a lesion is a necessary and sufficient cause. Criminal behaviour results from a combination of many factors related to the individual, the community and the environment, as well as any contribution from a brain injury. Of course, most people who suffer an injury to the brain do not subsequently engage in criminal behaviour of any kind, so can neuroscientific investigations shed light on which individuals, with which injuries, will act in a violent or antisocial manner?

In the recent systematic review published in the Proceedings of the National Academy of Sciences, a team of American and European researchers examined 17 cases in which a clear temporal relationship between a brain injury and the onset of criminal behaviour could be established. The patients’ lesions were identified and traced on a standardised brain atlas in order to investigate whether the lesion locations could be associated with a single circuit of neural connections.

The authors reported that although lesions associated with criminal behaviour were found in different regions of the brain, all were associated with a single connected network involving the lower part of the prefrontal cortex and the anterior part of the temporal lobes. In 16 of the 17 cases the lesions were further associated with another region of the prefrontal cortex and part of the basal forebrain.

Critically, each of these regions is important for two kinds of cognitive processes:

  • moral or value-based decision-making, which is the ability to weigh the value of specific actions and their effects; and
  • theory of mind, which is the capacity to understand another person’s point of view.

    These networks are not specifically associated with broader aspects of cognitive functioning. Hence one would not expect that these lesions would result in impairments of language, memory or general problem-solving abilities.

    Generally, the results of the review are consistent with recent neuropsychological work indicating that cognitive functions are not located in specific cerebral regions, but in connected networks of neurons distributed throughout the brain. While the study’s findings are insufficient to claim that criminal behaviour can be definitively associated with a particular lesion in an individual case, they point the way towards improvements in the way we might understand, predict and assign responsibility for criminal behaviour in those with an acquired brain injury.

    A/Prof Tim Hannan is Head of the School of Psychology at Charles Sturt University, and the Past President of the Australian Psychological Society.